Performance analysis of a LDPC coded multiple input/multiple output free-space optical system with Q-ary pulse-position modulation

The use of multiple laser transmitters combined with multiple photo detectors has the potential for combating fading effects on turbulent optical channels. In this paper, an analytical approach is presented to evaluate the bit error rate performance of a free space optical link using LDPC coded Q-ary optical PPM over atmospheric turbulence channel. Performance results are evaluated for multiple-laser and multiple photo-detector combination without and with LDPC code to combat the effect of atmospheric turbulence. The performance results are evaluated in terms of bit error rate (BER) and coding gain for several system parameters. It is found that LDPC coded system provides significant coding gain of 10 to 20dB over uncoded system can be evaluated at BER 10^-12 for multiple source and photo-detector combinations.